1. Field of the Invention (Technical Field)
The present invention relates to dielectric films, particularly dielectric films for use in wound capacitors, and specifically to a polymer-substrate film and method for making same.
2. Background Art
The development of high energy electrical storage systems with reduced size and weight are important for tactical and strategic pulsed power applications such as: electric armor, electric guns, particle beam accelerators, high power microwave sources and ballistic missile applications. In addition, commercially produced defibrillator systems have a significant need for higher energy density capacitors to achieve size and weight reductions. The dielectric energy storage density of pulsed power materials must be increased to provide feasibility or improve performance of these systems. The dielectric characteristics that represent a material's energy density are dielectric constant and operational electric field. Energy density is proportional to the dielectric constant and varies as the square of the electric field.
It is known to provide dielectric films incorporating polymers for use in capacitor production. However, with polymers having low physical strength, the full energy density potential cannot be realized because, at polymer thicknesses required for optimum performance (e.g. .ltoreq.8.0 .mu.m), the physical strength of a polymer film is insufficient for incorporation into a wound capacitor. At greater thicknesses, the polymer film's energy density reaches only a fraction of the polymer's potential due to the logarithmic decrease in dielectric strength associated with increasing polymer thickness. A need remains for a dielectric film featuring both optimal energy density as well as sufficient strength for incorporation, using conventional winding fabrication techniques, into capacitor devices. Against this background, the present invention was developed.